This application claims priority to Japanese Application No. 11-236,232, filed Aug. 24, 1999, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a marine drive, and more particularly to an improved drive shaft for a marine drive.
2. Description of Related Art
Outboard motors typically include a power head supported by a drive shaft housing. A clamping bracket usually secures the drive shaft housing to a transom of an associated watercraft. The drive shaft housing also supports a lower unit that includes a propeller or similar propulsion device. An engine within a cowling of the power head drives the propeller via a drive train. The drive train commonly includes a drive shaft, which extends generally vertically through the drive shaft housing, and a propeller shaft, which lies at about a 90 degree angle relative to the drive shaft. A transmission within the lower unit rotatably couples a lower end of the drive shaft to the propeller shaft.
The drive shaft is usually an elongate bar having an upper portion which couples to the crankshaft of the engine and a lower portion which couples to a gear of the transmission. The lower portion of the drive shaft also usually cooperates with support bearings and the like in order to maintain the drive shaft in a desired journaled mount orientation. An elongate waist portion is defined between the upper and lower portions of the drive shaft. The waist portion is generally free of connectors and various supporting mechanisms. Because of their support functions, the upper and lower portions are generally quite sturdy and have relatively large diameters. The waist portion has a somewhat smaller diameter than the upper and lower portions.
During watercraft operation, the propeller of the outboard motor may accidentally hit a rocky shoal or the like. When this happens, the propeller may be locked in position against a rock and may not be able to rotate even though the engine is still driving the propeller. This exerts a significant impact force on the drive train and can cause extensive damage to the transmission, drive shaft, crankshaft, etc. The waist portion of the drive shaft, with its relatively small diameter, acts to alleviate the impact force on the other components of the drive train. In essence, the waist portion provides a weak link so that the impact force will tend to twist the waist portion, which will absorb much of the impact force, rather than exposing the transmission and crankshaft to the impact force. Although this arrangement buffers much of the drive train from the impact force, it does not protect the drive shaft. As a result, the waist portion of the drive shaft can break or become damaged.
The present invention provides a drive shaft having a tapered waist portion that is designed to distribute impact forces along its entire length. This allows the waist portion to better absorb the impact force, inhibiting breakage or damage of the drive shaft when the watercraft hits a rocky shoal or the like and the propeller is locked in position with the engine still running.
In accordance with one aspect of the present invention, a marine propulsion unit comprises an engine adapted to drive an output shaft. The output shaft is drivingly engaged with a drive shaft. The drive shaft has a first end portion, a second end portion, and an elongate waist portion disposed between the first and second end portions. The first end portion is driven by the output shaft and the second end portion drives a propulsion device. The waist portion is tapered along its length.
In accordance with another aspect of the present invention, an outboard motor comprises an internal combustion engine adapted to drive a crankshaft. A drive shaft is provided and has a top end, a bottom end, and an elongate waist disposed between the top and bottom ends. The drive shaft top end is coupled to the crankshaft. The elongate waist is tapered so as to have a larger diameter towards the top end than towards the bottom end. The drive shaft bottom end drives a transmission. An output shaft is coupled to the transmission and drives a propulsion device.
In accordance with yet another aspect of the present invention, a drive shaft is provided for use in conjunction with a marine drive. The drive shaft has a first end portion adapted to be coupled to a crankshaft of an internal combustion engine, a second end portion adapted to drive a propulsion device, and an elongate waist portion disposed between the first and second end portions. The waist portion has a first end and a second end and is tapered so that a diameter of the waist portion at the first end is greater than a diameter of the waist portion at the second end.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follows.